Disconnectable mooring systems are used in combination or used to connect floating structures in harsh environment to sub sea structures. Fluid connections are provided in disconnectable mooring system. Connection-disconnection is realized by connection-disconnection of a subsea mooring buoy anchored to the seabed by catenary mooring lines. Fluid conduits from subsea wells extend into the mooring buoy and this mooring buoy is structurally connected to a floating structure, such as a tanker, by means of a hydraulic operated structural connection. On the tanker side a receiving means is provided for the mooring buoy and this receiving means is normally part of a turret structure in the floating structure such that this floating structure can rotate around the mooring buoy member during connection.
In the prior art subsea fluid conduits were slidably arranged in the mooring buoy member. The mooring buoy member and the receiving members were positioned relative to each other so that passages in both the mooring buoy member and the receiving member were aligned and connected with a structural connector. After that conduits were lifted through the passages in both the receiving member and the mooring buoy member and connected (possibly through quick connection means) to fluid conduits within the turret structure of the tanker.
Although this is a very straight forward and simple to realize method for connecting the mooring buoy member to the receiving members and to connect the fluid conduits from the well with conduits from the vessel problems arise during disconnect. During a disconnect situation the risers have to be disconnected and lowered to the mooring buoy member. Thereafter the structural connector can be reactivated to part the mooring buoy member from the receiving member. This is a time consuming operation. Increased disconnect situations, e.g. higher disconnect seastates, require a larger diameter disconnector to cope with the associated higher loads. Also given that the disconnection time should be reduced as much as possible and the number of risers conduits possibly increased connected to the subsea wells a prior art system cannot handle these requirements.
In U.S. Pat. No. 4,650,431 a disconnectable mooring system is described whilst U.S. Pat. Nos. 3,096,999, 3,353,595 and 4,337,971 relate to connectors.
Accordingly it is an object of the invention to provide an improved disconnectable mooring system in which connect-disconnect times can be shortened considerably without taking any risk with regard to safety precautions.
Another aim of the invention is to be able to use one single lifting line to bring the mooring buoy member and receiving member together wherein it is not longer necessary to have a number of separate lines for displaceing the conduits (risers) after connection has been realized.
A further aim of the invention is to realize a simple method of centering the mooring buoy member and the receiving member in a well defined way relative to each other.